Solar Tsunami Used To Measure Sun’s Magnetic Field

Asian Scientist (Jul. 12, 2013) - A solar tsunami observed by the Japanese Hinode spacecraft has been used to provide the first accurate estimates of the Sun's magnetic field.

Solar tsunamis are produced by enormous explosions in the Sun's atmosphere called coronal mass ejections (CMEs). As the CME travels out into space, the tsunami travels across the Sun at speeds of up to 1000 kilometers per second.

Similar to tsunamis on Earth, the shape of solar tsunamis is changed by the environment through which they move. Just as sound travels faster in water than in air, solar tsunamis have a higher speed in regions of stronger magnetic field. This unique feature allowed the team to measure the Sun's magnetic field.

Using data obtained using the Extreme ultraviolet Imaging Spectrometer (EIS), a instrument on the Japanese Hinode spacecraft, the team measured the density of the solar atmosphere through which the tsunami was traveling.

In their study, to be published in Solar Physics, the researchers analyzed data obtained using the Extreme Ultraviolet Imaging Spectrometer (EIS) based on the Japanese Hinode spacecraft. The EIS measures the speed of solar particles, and diagnoses the temperature and density of solar plasma - the ionized gas that surrounds the sun, its corona and beyond.

By measuring the density of the solar atmosphere through which the tsunami was traveling, the researchers were able to determine the strength of the magnetic field which permeates the Sun's atmosphere.

"We've demonstrated that the Sun's atmosphere has a magnetic field about ten times weaker than a normal fridge magnet," said Dr David Long, lead author of the study.

Visible as loops and other structures in the Sun's atmosphere, the Sun's magnetic field is difficult to measure directly and usually has to be estimated using intensive computer simulations. It was thought to be too weak to detect until researchers turned to the three highly sensitive telescopes on the Hinode spacecraft.

The instruments on Hinode act like a microscope, using visible, X-ray and ultraviolet light to track how the magnetic field around sunspots is generated, shapes itself, and then fades away.

Led by the Japan Aerospace Exploration Agency (JAXA), the Hinode mission is a collaboration between the space agencies of Japan, the United States, the United Kingdom and Europe.